Chapter 4 Networking and the Internet © 2007 Pearson Addison-Wesley. All rights reserved.

Chapter 4

Networking and the Internet

© 2007 Pearson Addison-Wesley.All rights reserved

© 2007 Pearson Addison-Wesley. All rights reserved 0-2

Chapter 4: Networking and the Internet

• 4.1 Network Fundamentals

• 4.2 The Internet

• 4.3 The World Wide Web

• 4.4 Internet Protocols

• 4.5 Security


Network Classifications

• Scope– Local area network (LAN)– Metropolitan area (MAN)– Wide area network (WAN)

• Ownership– Closed versus open

• Topology (configuration)– Ring– Bus– Star


Figure 4.1 Network topologies


Figure 4.1 Network topologies (continued)


List of Problems (so far)

• Topologies

• Framing

• Error control

• Flow control

• Multiple access– How to share a wire


Protocols

• Token ring– Popular in ring networks– Possession of token provides right to introduce new

message

• CSMA/CD– Used in Ethernet– Silent bus provides right to introduce new message


Figure 4.2 Communication over a ring network


Figure 4.3 Communication over a bus network


Connecting Networks

• Repeater: Extends a network

• Bridge: Connects two compatible networks

• Switch: Connect several compatible networks

• Router: Connects two incompatible networks resulting in a network of networks called an internet


Figure 4.4 Building a large bus network from smaller ones


Figure 4.5 A router connecting a bus network to a star network


Inter-process Communication

• Client-server– One server, many clients– Server must execute continuously– Client initiates communication

• Peer-to-peer (P2P)– Two processes communicating as equals– Peer processes can be short-lived


Figure 4.6 The client/server model compared to the peer-to-peer model


Distributed Systems

• Systems with parts that run on different computers– Infrastructure can be provided by standardized

toolkits• Example: Enterprise Java Beans from Sun Microsystems

• Example: .NET framework from Microsoft


The Internet

• The Internet: An internet that spans the world– Original goal was to develop a means of connecting

networks that would not be disrupted by local disasters.

– Today it has shifted from an academic research project to a commercial undertaking.


Internet Architecture

• Domain: A portion of the Internet that network or internet controlled by a single authority– Connected to the rest of the Internet (the cloud) by a

router called a gateway

• Internet Corporation for Assigned Names & Numbers (ICANN): Oversees the registration of domains

• Domain Name (www.cs.gsu.edu)


Figure 4.7 A typical approach to connecting to the Internet


Strategies for connecting to the Internet

• Internet Service Provider (ISP): Provides connectivity to the Internet

• Popular means of connecting:– Traditional telephone (dial up connection)– Cable connections– DSL (Digital Subscriber Line )– Wireless


Internet Addressing: IP Addresses

• IP address: 32 bit identifier for a machine (currently being expanded to a 128 bit system)– Network identifier: Assigned by ICANN– Host address: Assigned by domain administrator

• Dotted decimal notation: Common notation for displaying IP addresses– Example: 192.207.177.133


Internet Addressing: Host Names

• Mnemonic address made up of two parts:– Domain name

• Assigned by a registrar• Example: gsu.edu• Top level domain: Classification of domain owner

– By usage – Example: .com = commercial– By country – Example: .au = Australia

– Subdomains and individual host names• Assigned by domain owner• Example: r2d2.compsci.nowhereu.edu

• Translation between mnemonic addresses and IP addresses handled by name servers

.


Traditional Internet Applications

• Electronic Mail (email)– Domain mail server collects incoming mail and

transmits outing mail– Mail server delivers collected incoming mail to

clients via POP3 or IMAP

• File Transfer Protocol (FTP)

• Telnet and SSH


Internet Software Layers

• Application: Constructs message with address

• Transport: Chops message into packets

• Network: Handles routing through the Internet

• Link: Handles actual transmission of packets


Figure 4.12 Package-shipping example


Figure 4.13 The Internet software layers


Figure 4.14 Following a message through the Internet


Layering: logical communication

applicationtransportnetwork

link


link


link


link

networklink

physical

data

data

E.g.: transport

• take data from app• add addressing,

reliability check info to form “datagram”

• send datagram to peer

• wait for peer to ack receipt

• analogy: post office

data

transport

transport

ack


Layering: physical communication


link


link


link


link

networklink

data

data


Protocol layering and data

Each layer takes data from above• adds header information to create new data unit

(“encapsulation”)• passes new data unit to layer below

source destination

datagram


link


link

M

M

M

M

Ht

HtHn

HtHnHl

M

M

M

M

Ht

HtHn

HtHnHl

message

segment

frame


Applications and app-layer protocols

Application: communicating, distributed processes– running in network hosts in “user

space”– exchange messages to implement

app– e.g., email, file transfer, the Web

Application-layer protocols– one “piece” of an app– define messages exchanged by

apps and actions taken– user services provided by lower

layer protocols

application

transportnetworkdata link

application


application



Network applications: some jargon

• A process is a program that is running within a host.

• Within the same host, two processes communicate with interprocess communication defined by the OS.

• Processes running in different hosts communicate with an application-layer protocol

• A user agent is an interface between the user and the network application.– Web:browser

– E-mail: mail reader

– streaming audio/video: media player


Application-layer protocols

API: application programming interface

• defines interface between application and transport layer

• socket: Internet API– two processes

communicate by sending data into socket, reading data out of socket

Q: how does a process “identify” the other process with which it wants to communicate?– IP address of host

running other process– “port number” - allows

receiving host to determine to which local process the message should be delivered


TCP/IP Protocol Suite

• Transport Layer– TCP– UDP

• Network Layer– IP (IPv4 and IPv6)


Figure 4.15 Choosing between TCP and UDP


Security

• Attacks– Malware (viruses, worms, Trojan horses, spyware, phishing

software)– Denial of service– Spam

• Protection– Firewalls– Spam filters– Proxy Servers– Antivirus software


Encryption

• FTPS, HTTPS, SSL

• Public-key Encryption– Public key: Used to encrypt messages– Private key: Used to decrypt messages

• Certificates and Digital Signatures


Figure 4.16 Public-key encryption


World Wide Web

• Hypertext and HTTP

• Browser gets documents from Web server

• Documents identified by URLs


Figure 4.8 A typical URL


Hypertext Document Format

• Entire document is printable characters• Contains tags to communicate with browser

– Appearance • <h1> to start a level one heading

• <p> to start a new paragraph

– Links to other documents and content• <a href = . . . >

– Insert images• <img src = . . . >


Figure 4.9 A simple Web page


Figure 4.9 A simple Web page (continued)


Figure 4.10 An enhanced simple Web page


Figure 4.10 An enhanced simple Web page (continued)


Extensible Markup Language (XML)

• XML: A language for constructing markup languages similar to HTML– A descendant of SGML– Opens door to a World Wide Semantic Web


Using XML

<staff clef = “treble”> <key>C minor</key>

<time> 2/4 </time>

<measure> < rest> egth </rest> <notes> egth G,

egth G, egth G </notes></measure>

<measure> <notes> hlf E </notes></measure>

</staff>


Figure 4.11 The first two bars of Beethoven’s Fifth Symphony


Client Side Versus Server Side

• Client-side activities– Examples: java applets, javascript, Macromedia

Flash

• Server-side activities– Common Gateway Interface (CGI)– Servlets– PHP

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